The ability to differentiate between rewards and losses is critical for motivated action, and aberrant reward and loss processing has been associated with psychopathology. The reward positivity (RewP) and feedback negativity (FN) are ERPs elicited by monetary gains and losses, respectively, and are promising individual difference measures. However, few studies have reported on the psychometric properties of the RewP and FN—crucial characteristics necessary for valid individual difference measures. The current study examined the internal consistency and 1‐week test‐retest reliability of the RewP and FN as elicited by the doors task among 59 young adults. The RewP, FN, and their difference score (ΔRewP) all showed significant correlations between Time 1 and Time 2. The RewP and FN also achieved acceptable internal consistency at both time points within 20 trials using both Cronbach's α and a generalizability theory‐derived dependability measure. Internal consistency for ΔRewP was notably weaker at both time points, which is expected from two highly intercorrelated constituent scores. In conclusion, the RewP and FN have strong psychometric properties in a healthy adult sample. Future research is needed to assess the psychometric properties of these ERPs in different age cohorts and in clinical populations.